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26 Cards in this Set

  • Front
  • Back
What are potential sources for TCA cycle?
Oxidized carbohydrates
Fatty Acids
Ethanol (as Acetyl CoA
Amino Acids
What energy substrates are produced during TCA?

Small amount of GTP
Where does the TCA cycle occur?
In mt of aerobic cells
Starting materials for TCA?
Carbon sources (2 Carbon units of Acetyl CoA)
What product is recylced?
How is TCA regulated?
Isocitrate Dehydrogenase is the main regulatory enzyme
Enzymes involved in TCA cycle?
Citrate synthase
NADH producing dehydrogenases
FADH producing dehydrogenase
What role does Co-enzyme A (CoA-SH) play? Cofactors needed?
Requires dietary panthothenic acid
Co-enzyme A transfers/activ. acyl groups in TCA
Cleavage of thioester bond large -G drive rxn
What vitamin does NAD require?
Requires niacin. 3 of dehydrogenase rxn have NAD cofactors
What vitamin does FAD require? Enzyme involved with
Reduced to FADH2
Succinate Dehydrogenase
What cofactors are utilized by a-ketoglutarate dehydrogenase?
Alpha-keto Dehydrog is also a decarboxylase and utilizes:
thiamine pyrophosphate TPP
Lipoic acid- from lipoamide
What enzymes reg TCA?
isocitrate dehydrogenase
rate limiting occurs after branch point for removing citrate for FA Synthesis
Isocitrate regulation factors?
Activated: by isocitrate and ADPsubstrate feed forward
Calcium and muscle contraction in muscle

Inhibited: FBack by NADH
Is TCA open or closed cycle?
Open: compnds enter and leave at many points
What is the rate limiting step of TCA cycle?
Isocitrate dehydrogenase
Where does Isocitrate dh occur in TCA?
After citrate has been removed for FA synthesesis leaving isocitrate.
Isocitrate--->alpha-ketoglutarate by isocitrate DH
Regulation of isocitrate DH?
Activated: Isocitrate
Calcium (especilly in muscle)
Inhibited: ADP and NADH
What is the fate of AA carbons in the TCA cycle during fed state? fast state?
During the fed state carbons are catabolized to CO2 and converted to FA for storage as TG.

Fast: Used in gluconeogenesis (glucogenic amino acids) or further catabolized to CO2 (ketogenic AA).
What three molecules can be transaminated?
Pyruvate-> Alanine 3C
Oxaloacetate-> Aspartate 4C
A-ketoglutarate-> Glutamate 5
How can AA and FA carbons enter the TCA cycle as Succinyl CoA?
Propionyl CoA is converted to Suc CoA

Propionyl CoA is product of add chain FA catabolism and AA catabolism
What molecule is precursor for Gluconeogensis?
Oxaloacetate carbons
How do oxaloacetate carbons get into cytosol from mt since mt membrane is impermeable to oxalo?
Oxalo is converted to either malate by malate DH or aspartate by transamination. Once in cytosol it is converted back to oxalo by cytosolic form
If an AA is brought into the TCA cycle after a-ketoglutarate can it be gluconeogenic?
Yes, but if brought into cycle before a-Ketoglutarate then 2-carbons are lost
What can Succinyl CoA be used for when leaving TCA?
Used for heme synthesis in lever and reticulocytes
What molecule leaves the TCA for glutamate synthesis (transamination), glutamine synthesis from glutamate, and neurotransmitter synthesis (glutamate and GABA)?
What is fate of citrate that leaves the TCA cycle?
In the liver citrate crosses the mt membrane, converted to Acetyl CoA for FA synthesis. occurs during Fed state

The citrate is produced from excess glucose and AA. The channel is an obligatory link between glycolysis and FA synthesis from carbohydrates